High resolution c.r. tube



y 1962 E. o. STONE ETAL HIGH RESOLUTION C.R. TUBE Filed April 29, 196000000000000.ooofioooi oQ 32.22.2232.235 .9 a

IN VE/VTORS Elmer 0. 570m dim Z Kayla BY a QMQS e 2.33. 3: z..:{5353.53: w vv%.:

3. .,.H. ...u nvvv A TTORNE Y United States Patent Ofiice 3,036,238Patented May 22, 1962 3,036,238 HIGH RESOLUTION C.R. TUBE Elmer 0.Stone, Seneca Falls, and Alan T. Kuryla, Ge-

neva, N.Y., assignors to Sylvania Electric Products Inc., a corporationof Delaware Filed Apr. 29, 1960, Ser. No. 25,596 6 Claims. (Cl. 315-16)This invention relates to cathode ray tubes and in particular to the gunconstruction thereof to produce a high resolution cathode ray beam onthe screen of the tube.

The resolution of a trace or picture on the face of a screen isdetermined in part by the cross sectional size and shape of the electronbeam. The trace on the screen can be no finer than the image of thecathode spot itself, or, Where a convergent electron lens is employed,of the image of the cathode spot at a cross over point of the rays fromopposite diametrical points on the cathode. To maintain the beam againstspreading and the spot image on the screen as small as possible, aconvergent electronic lens is placed close to the cathode, and Wehneltcylinders are employed to keep the resultant beam confined; in general,the longer these cylinders are, the better the resolution of thepicture. However, in order to shorten the overall length of cathode raytubes, the gun, too, has to be shortened. Various expedients have beenemployed to obtain a proper beam form and cross section with theshortened gun. Also to reduce cost and simplify the circuitry involvingthe formation of a picture on the screen of the tube, electrostaticfocusing of the beam has been resorted to. This involves the creation ofa second electron lens at a distance from the lens close to the cathode.

One form of gun involving the dual lens structure wherein the secondlens is designed to have excellent focus characteristics regardless ofchanges in anode voltage and to have increased depth of focus over asimple bipotential lens, is exemplified in the patents to Hoagland Re.24,673, granted July 28, 1959, and Collins et al. 2,922,072, grantedJanuary 19, 1960.

The optimum sizes of parts and spacing between them is given in thesepatents to which reference may be had for further details.

It is found that with a different arrangement of potentials on thevarious electrodes then previously known in the art, the spot size ascast on the screen and therefore the resolution of the image may begreatly improved.

It is an object of this invention to provide a cathode ray tube with agun structure and circuitry such as to produce a beam of electrons ofvery small diameter at the screen of the tube.

More specifically, it is an object of this invention to provide a fine.trace or picture 011 the screen of a cathode ray tube of the typehaving spaced electron lenses and wherein the lens most remote from thesource of elec trons or cathode is surrounded by a focusing anode withdifferent potentials applied to each part of the most remote lens.

Other objects will become apparent upon further consideration of thefollowing specification and claims, when taken in connection with theaccompanying drawing in which the figure diagrammatically illustrates acathode ray tube with a gun structure and associated circuitry, inaccordance with the invention.

On the figure, 10 represents the glass envelope with aquadag coating 12,as is usual in the art, extending to a high voltage button 14 to which adirect current high voltage lead 16 is connectible. The aquadag coatingextends some distance into the neck 18 of the envelope. The gun iscomprised of a cathode and first grid assembly 22 such as is shown, forexample, at 10 in the Johnson et al. Patent 2,864,935, granted December16, 1958.

Spaced longitudinally from the first grid of the assembly is a secondgrid 24 and spaced longitudinally from that is the first or acceleratinganode 26. The gun structure may include a bent gun or slash gun featureto trap ions as is known in the prior art. Spaced from the acceleratingor first anode 26 is a third anode 28 and surrounding and overlappingthe first and third anodes or riding saddle on the first and thirdanodes is the second, cylindrical anode 30.

The whole group comprised of cathode assembly with its first grid, thesecond grid and the anodes are supported Within the tube neck bysuitable supports, not shown, and all of the grids and anodes are heldin proper spaced relation to each other by means of a number ofinsulator bars 32 of glass or equivalent insulating material connectedby pins 34 to the various electrodes. All the electrodes areindividually connected to terminals; the third anode 28, incontradistinction to the prior art, is connected to a terminalindependently of the first anode 26. As here shown, the third anode isconnected via conductive snubbers or springs 36 to the conductivecoating 12 within the envelope. If desired, the third electrode may beconnected via a lead to a pin terminal extending from the base of thetube. A conventional deflecting coil assembly 38 surrounds the neck ofthe tube.

For the gun to operate to bring the spot size on the screen toapproximately one half of that which results thereon where anodes 26 and28 are at the same potential, it is desirable to apply a much highervoltage to the third anode than to the first anode. In actual practice,with the proportions of parts set forth in the Hoagland and Collins etal. patents referred to above, the voltage applied to the first anodeshould be approximately one-fourth to onefifth the voltage applied tothe third anode. With 16 kv. applied to the third anode, 3500 v. wouldbe suitable for application to the first anode; the focus controlvoltage on the second anode could be anywhere between Zero "olts and1500 volts, as required to obtain a suitable spot on the screen. Withthese voltages, a normal voltage of 300 or approximately onefiftieth ofthat applied to the third anode is applied to the second grid with oneof the pair including cathode and control grid at zero potential and theother of the pair at signal potential.

As stated before, by the arrangement described and with the voltagesapplied to the electrodes as set forth, a spot size on the screen isattained which is much smaller than could be attained where the firstand third anodes are at the same potential.

As an explanation of this, consider the analogy between the electronlenses of the invention and optical lenses. The lens formed by grid 22and grid 24 creates a cross over point between the two or a virtualimage of the cathode closely in front ofthe bottom 40 of the secondgrid. The second lens formed by the three anodes 26, 28 and 30 can beregarded as seeing either this cross over or the virtual image. Let oneof these be regarded as lying in the object plane. The image plane ofthe second lens is on the screen. The magnification of the object in theobject plane on the screen is the ratio of the distance between theobject and lens and the distance between the lens and the image plane.If a be the distance between the object plane and the effective centerof the second lens and b be the distance between the eifective center ofthe lens and the image plane, then the magnification is equal to theinverse ratio of these distances. This can be expressed as bmagnification Thus to secure a small spot on the screen it isadvantageous to make the distance a as large as possible. This can beachieved, in the prior art, by lengthening the first anode but thiswould lengthen the neck of the tube, which is undesirable. Actually, inthe prior art, the voltage on the first anode was much higher than thevoltage on the second grid, making a very strong lens which drove theobject plane closer to the first lens and therefore shortened thedistance a and made the magnification larger. With the applied voltagesof the invention to the arrangement arrangement 26, 28 and 30.Furthermore, in order to lengthen the efiective distance a as much aspossible the first lens, that is, the lens formed between the secondgrid and first anode, is weakened by reducing the voltage on the firstanode to about one fourth of that on the third anode.

Thus while retaining the desirable features of a saddle type of lens,i.e., one utilizing an anode overlapping two other anodes with theattendant advantages of constant focus regardless of normal anodevoltage changes and with the advantage of its depth of focus, byapplying the different voltages to these anodes, increased spotresolution is attained. This is enhanced by decreasing the voltage onthe first anode, thereby increasing the distance from the object planeto the second lens.

Having thus described the invention, what is claimed is:

1. A cathode ray tube system including a gun having electrodes includinga cathode, a grid, a second grid, and first, second and third anodes,said first, second and third anodes being spaced in that order in thedirection away from the second grid; said first and third anodes beingin axial alignment and spaced from each other with the second anoderiding saddle over the first and third anodes, leads to each of theelectrodes, the leads to the grids and the first and third anodes beingindependent ofeach other,

and means for coupling voltages to the various electrodes, the voltageto the third anode being higher than that applied to the first anode.

2. A cathode ray tube system including a gun having dependent of eachother, and means for coupling voltages to the various electrodes, thevoltage to the third anode being higher than that applied to the firstanode.

3. A cathode ray tube system including a gun having electrodes includinga cathode, a grid, a second grid, and first, second and third anodes,said first, second and third anodes being spaced in that order in thedirection away from the second grid; said first and third anodes beingin axial alignment and spaced from each other with the second anoderiding saddle over the first and third anodes, leads to each of theelectrodes, the leads to the grids and the first and third anodes beingindependent of each other, and means for supplying voltages to thevarious leads, the voltage to the leads of the thirdanode being four tofive times that applied to the lead of the first anode.

4. A cathode ray tube system including a gun having electrodes includinga cathode, a first grid, a second grid, and first, second and thirdanodes, said first, second and third anodes being spaced in that orderin the direction away from the second grid; said cathode, grids, firstand third anodes being in axial alignment and spaced from each otherwith the second anode riding saddle over the first and third anodes,leads to each of the electrodes, the leads to the grids and the firstand third anodes being independent of each other, and means forsupplying voltages to the various leads, the voltage to the leads of thethird anode being four to five times that applied to the lead of thefirst anode. V I

' 5. A cathode raytube system including a gun having electrodesincluding a cathode, a grid, a second grid, and first, second and thirdanodes, said first, second and third anodes being spaced in that orderin the direction away from the second grid; said first and third anodesbeing in axial alignment and spaced from each other with the secondanode riding saddle over the first and third anodes,

leads to each of the electrodes, the leads to the grids and the firstand third anodes being independent of each other, the voltage to thelead of the third anode being approximately five times that applied tothe lead of the first anode and the voltage applied to the lead of thesecond grid being approximately one-fiftieth of the voltage applied tothe third anode.

6. A cathode ray tube system including a gun having electrodes includinga cathode, a first grid, a second grid,

and first, second and third anodes, said first and second third anodesbeing spaced in that order in the direction away from the second grid;said cathode, grids, first and third; anodes being in axial alignmentand spaced from each other with the second anode riding saddle over thefirst and third anodes, leads to each of the electrodes, the leads tothe grids and the first and third anodes being independent of eachother, the voltage to the lead of the third anode being four to fivetimes that applied to the lead of the first anode and the voltageapplied to the lead of the second grid being approximately one-fiftiethof the voltage applied to the third anode.

' References Cited in the tile of this patent UNITED STATES PATENTS2,719,243 Hoagland Sept. 27, 1955 2,732,511 Dichter a; Jan. 24, 19562,839,703. Niklas June 17, 1958 2,902,6Q3 Knechtli Sept. 1, 19592,963,608;

Benda et al. Dec. 6, 1960

